Cloud Auto Join

client/driver/env: interpolate empty optional meta params as empty strings

client/driver: remove unused const 'dockerPullProgressEmitInterval'

Fix deadlock in deadline timer logic when progress deadline is passed and the deployment is updated.

Fix the initial progress deadline calculation when the alloc is inplace updated to be part of a new deployment

Guard against Canary being set to false at the same time as an
allocation is being stopped: this could cause RemoveTask to be called
with the wrong Canary value and leaking a service.

Deleting both Canary values is the safest route.

Also refactor Consul ServiceClient to take a struct instead of a massive
set of arguments. Meant updating a lot of code but it should be far
easier to extend in the future as you will only need to update a single
struct instead of every single call site.

Adds an e2e test for canary tags.